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Hello everyone, this is my first post on this forum. Just bought my first Z3, it is a 1996 1.9. I bought for a daily driver back and forth to work. I was amazed at the gas mileage 34.5. I picked it up from a private owner in Oklahoma, this was a one owner car, with 138,000 miles on it. No dents a few small scratches, but that doesn't matter because I am going to paint it Yellow, I have always wanted a yellow roadster. I will post pictures of before and after pic's. Owner said he always ran 87 oct in her. So I thought I would put some 89 in her. Wow what a difference. I lost 8mpg with 89. Went back to 87 and mpg came back. The only think I found wrong with this car is:

It needs brake pad sensors
Has a rough idle when cold

I didn't think this was to bad for $6150.
Again I bought it for a daily driver, it is 68.1 miles to work one way each morning. So I was worried about it mileage. Oh yeah the speedometer is off about 3 mph when I am running 75 by the speedometer it is really running 72.

I will post pic's what she will look like when I get her painted, when I am able to post pic's. My painter has 1 car in front of me. Does anyone know what color yellow this is?

... Owner said he always ran 87 oct in her. So I thought I would put some 89 in her. Wow what a difference. I lost 8mpg with 89. Went back to 87 and mpg came back....

The Owners Manual says the car is rated (for official horsepower and mileage) on 89 octane, can tolerate 87 octane, and will have increased performance on 91-93 octane. I doubt that using the 89 octane the engine was made to run on could have been the sole cause of the loss in mileage. It could have been variations in driving or filling or even a miscalculation. For consistency I would try a few tanks of 89 back to back, and then a few tanks of 93, before concluding that 87 was best. The 87 octane reduces power as the knock sensor is reducing ignition advance to prevent pinging. This may not matter in a commute.